Science, Tech, Math › Science Cool Chemical Element Facts Share Flipboard Email Print Joachim Angeltun / Getty Images Science Chemistry Periodic Table Basics Chemical Laws Molecules Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated May 06, 2019 A chemical element is a form of matter that can't be broken into smaller pieces by any chemical reaction. Essentially, this means elements are like different building blocks used to construct matter. At present, every element in the periodic table has been discovered or created in a lab. There are 118 known elements. If another element, with a higher atomic number (more protons) is discovered, another row will need to be added to the periodic table. Elements and Atoms A sample of a pure element consists of one type of atom, which means each atom contains the same number of protons as every other atom in the specimen. The number of electrons in each atom can vary (different ions), as can the number of neutrons (different isotopes). Two samples of the exact same element may look completely different and exhibit different chemical and physical properties. This is because the atoms of the element can bond and stack in multiple ways, forming what are called allotropes of an element. Two examples of allotropes of carbon are diamond and graphite. The Heaviest Element The heaviest element, in terms of mass per atom, is element 118. However, the heaviest element in terms of density is either osmium (theoretically 22.61 g/cm3) or iridium (theoretically 22.65 g/cm3). Under experimental conditions, osmium is almost always more dense than iridium, but the values are so close and dependent on so many factors, it really makes no difference. Both osmium and iridium are about two times heavier than lead! The Most Abundant Elements The most abundant element in the universe is hydrogen, accounting for about 3/4 of the ordinary matter scientists have observed. The most abundant element in the human body is oxygen, in terms of mass, or hydrogen, in terms of atoms of an element present in the highest quantity. The Most Electronegative Element Fluorine is best at attracting an electron to form a chemical bond, so it readily forms compounds and participates in chemical reactions. This makes it the most electronegative element. At the opposite end of the scale is the most electropositive element, which is the one with the lowest electronegativity. This is the element francium, which does not attract bonding electrons. Like fluorine, the element is extremely reactive, too, because compounds most readily form between atoms that have different electronegativity values. The Most Expensive Elements It's difficult to name the most expensive element because any of the elements from francium and higher atomic number (the transuranium elements) decay so quickly they can't be collected to be sold. These elements are unimaginably expensive because they are produced in a nuclear laboratory or reactor. The most expensive natural element you could actually buy would probably be lutetium, which would run around $10,000 for 100 grams. Conductive and Radioactive Elements Conductive elements transfer heat and electricity. Most metals are excellent conductors, however, the most conductive metals are silver, followed by copper and gold. Radioactive elements release energy and particles via radioactive decay. It's hard to say which element is the most radioactive, as all elements higher than atomic number 84 are unstable. The highest measured radioactivity comes from the element polonium. Just one milligram of polonium emits as many alpha particles as 5 grams of radium, another highly radioactive element. Metallic Elements The most metallic element is the one which displays traits of metals to the highest extent. These include the ability to be reduced in a chemical reaction, the capacity to form chlorides and oxides, and the ability to displace hydrogen from dilute acids. Francium is technically the most metallic element, but since there are only a few atoms of it on Earth at any given time, cesium deserves the title.